A photoelectrochemical cell device consists essentially of an electrolyte containing appropriately chosen redox couples in contact with a working electrode voltage-biased with respect to a convenient reference electrode and in series with a counterelectrode, which, upon illuminating the working electrode with light of the proper wave lengths, converts the introduced redox couples to a higher energy state and creates an externally measureable current with net positive efficiency. Such a working electrode has been termed a photoelectrode.
The application of semiconductor materials for photoelectrochemical conversions has been studied at least since 1972 when it was first reported that water could be split into hydrogen and oxygen in the presence of illuminated, doped TiO.sub.2 crystals [K. Honda and A. Fujishima, Nature, 238, 38 (1972)]. Further research has focussed predominantly on crystalline systems; e.g., c-Si [D. Laser and A. J. Bard, Journal of Physical Chemistry, 80, 459 (1976)], c-GaAs [B. Miller, F. A. Thiel, and A. Heller, Applied Physics Letters, 38, 282 (1981)].
Little investigation has been reported on vitreous systems despite several inherent advantages possessed by glasses, viz., readily adjustable compositions, easy formability, and good strength. It is believed this lack of research has been due at least in part from traditional emphases on the simple, regular structures of crystals. Furthermore, a-Si was discovered to contain high densities of defect states associated with "dangling" bonds [A. E. Owen and W. E. Spear, Physics and Chemistry of Glasses, 17, (5) 174 (1976)]. Those defects were expected to lower photocarrier mobility by trapping, thereby reducing photocurrent density. That expectation has generally been extended to all glass compositions. Finally, doped crystalline semiconductors can conventionally exhibit electrical resistivities below 10 ohm-cm, whereas glasses commonly demonstrate electrical resistivities above 10.sup.8 ohm-cm.
Yet, the intrinsic advantages in formability, coupled with the absence of grain boundaries, have led to the extensive use of amorphous materials in electronic devices and in the production of high durability substrates. A recognition of those advantages resulted in research being initiated to determine their applicability as photoelectrodes in photoelectrochemical cell devices for solar energy conversion. A cornerstone of the investigation has been an endeavor to exploit physical property-glass composition interdependencies. Hence, it was perceived that multicomponent amorphous semiconductors could offer an adjustable spectrum of physical properties not fundamentally attainable from single element materials. Furthermore, laminates of varying composition, i.e., a graded gap junction, can be perceived which are capable of attaining efficiencies exceeding any value possible for a single gap junction.